diff --git a/libcxx/include/__bsd_locale_fallbacks.h b/libcxx/include/__bsd_locale_fallbacks.h
--- a/libcxx/include/__bsd_locale_fallbacks.h
+++ b/libcxx/include/__bsd_locale_fallbacks.h
@@ -108,7 +108,7 @@
 }
 #endif
 
-inline
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 4, 5)
 int __libcpp_snprintf_l(char *__s, size_t __n, locale_t __l, const char *__format, ...) {
     va_list __va;
     va_start(__va, __format);
@@ -118,7 +118,7 @@
     return __res;
 }
 
-inline
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 3, 4)
 int __libcpp_asprintf_l(char **__s, locale_t __l, const char *__format, ...) {
     va_list __va;
     va_start(__va, __format);
@@ -128,7 +128,7 @@
     return __res;
 }
 
-inline
+inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_ATTRIBUTE_FORMAT(__scanf__, 3, 4)
 int __libcpp_sscanf_l(const char *__s, locale_t __l, const char *__format, ...) {
     va_list __va;
     va_start(__va, __format);
diff --git a/libcxx/include/__config b/libcxx/include/__config
--- a/libcxx/include/__config
+++ b/libcxx/include/__config
@@ -1352,10 +1352,11 @@
 #endif
 
 #if defined(__GNUC__) || defined(__clang__)
-#define _LIBCPP_FORMAT_PRINTF(a, b)                                            \
-  __attribute__((__format__(__printf__, a, b)))
+  // The attribute uses 1-based indices.
+# define _LIBCPP_ATTRIBUTE_FORMAT(archetype, format_string_index, first_format_arg_index) \
+    __attribute__((__format__(archetype, format_string_index, first_format_arg_index)))
 #else
-#define _LIBCPP_FORMAT_PRINTF(a, b)
+# define _LIBCPP_ATTRIBUTE_FORMAT(archetype, format_string_index, first_format_arg_index) /* nothing */
 #endif
 
 #endif // __cplusplus
diff --git a/libcxx/src/filesystem/filesystem_common.h b/libcxx/src/filesystem/filesystem_common.h
--- a/libcxx/src/filesystem/filesystem_common.h
+++ b/libcxx/src/filesystem/filesystem_common.h
@@ -60,7 +60,7 @@
 
 namespace {
 
-static _LIBCPP_FORMAT_PRINTF(1, 0) string
+static _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 0) string
 format_string_impl(const char* msg, va_list ap) {
   array<char, 256> buf;
 
@@ -84,7 +84,7 @@
   return result;
 }
 
-static _LIBCPP_FORMAT_PRINTF(1, 2) string
+static _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 1, 2) string
 format_string(const char* msg, ...) {
   string ret;
   va_list ap;
@@ -172,7 +172,7 @@
     _LIBCPP_UNREACHABLE();
   }
 
-  _LIBCPP_FORMAT_PRINTF(3, 0)
+  _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 3, 0)
   void report_impl(const error_code& ec, const char* msg, va_list ap) const {
     if (ec_) {
       *ec_ = ec;
@@ -191,7 +191,7 @@
     _LIBCPP_UNREACHABLE();
   }
 
-  _LIBCPP_FORMAT_PRINTF(3, 4)
+  _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 3, 4)
   T report(const error_code& ec, const char* msg, ...) const {
     va_list ap;
     va_start(ap, msg);
@@ -213,7 +213,7 @@
     return report(make_error_code(err));
   }
 
-  _LIBCPP_FORMAT_PRINTF(3, 4)
+  _LIBCPP_ATTRIBUTE_FORMAT(__printf__, 3, 4)
   T report(errc const& err, const char* msg, ...) const {
     va_list ap;
     va_start(ap, msg);